This invention relates generally to speed reducers and, more particularly, to a two-stage speed reducer capable of achieving very high reduction ratios, and including a planocentric gear arrangement having an output ring gear and an eccentric planet gear which is axially adjustable with respect to the ring gear to allow for backlash adjustment between the gears from outside the gearbox.
Speed reducers for achieving extremely high reduction radios have been proposed in the past and these commonly include primary and secondary reduction stages, with at least one of those stages being a planocentric gear arrangement. A typical prior art gear reducer is illustrated in U.S. Pat. No. 4,440,044.
The planocentric gear arrangement commonly includes an output ring gear and a planet gear, with the planet gear having only a few teeth less than the number of teeth on the ring gear. For example, it is not unusual for the planet gear to have only one to four teeth less than the teeth on the ring gear to provide for maximum reduction of speed from the planet gear to the ring gear. Consequently, the gear teeth must be precisely machined and the gears must be carefully assembled with sufficient clearance to avoid an interference condition, but yet must not be provided with excessive clearance that will produce a backlash condition.
In addition, over a period of time, as the ring gear and planet gear run together, the mating teeth surfaces become worn and excessive backlash develops within the gear arrangement.